Integrated circuit optical sensors are increasingly used to provide visual input for control systems as well as in cameras. Many applications place optical sensors in harsh environments, requiring that the sensors be enclosed in a protective package. Presently, commercial optical sensor packages are developed from conventional semiconductor packages incorporating clear plastic or add-on windows to conventional molded or ceramic devices. These packaging assemblies are expensive and difficult to manufacture.
An optical sensor may be used in applications exposing the sensor to a range of light intensities beyond the dynamic range of the sensor. As an example, a configuration allowing the sensor to operate at low light levels may cause the sensor to wash out at a high light level. As another example, consider a scene illuminated by florescent lighting, which cycles in intensity with the alternating current supply. A pixel array sensor with a high scan rate will have portions of each frame illuminated by varying levels of light. To avoid this problem, an integration period of at least approximately 30 milliseconds must be used. Since the scan time is generally a multiple of the integration time, a camera set to 30 milliseconds scan period for a bright scene may result in an excessively long scan time for a dim scene. Further, particularly if a lens is used to focus light on the sensor, direct exposure to sunlight can generate sufficient heat to damage sensor elements.
Mechanical or electromechanical shutters, when used, are not typically part of the optical sensor package. Electrically attenuated grayscale filters are never part of the commercial sensor device package, if available at all.
What is needed is a package for protecting an optical sensor that is inexpensive and easy to manufacture. The package should be adaptable to include an electronically controlled variable attenuator.